Constraint relaxation leads to jamming

TL;DR

This paper reveals that adding transitions to out-of-equilibrium systems can paradoxically reduce activity, leading to jamming, contrary to expectations based on equilibrium system behavior.

Contribution

It demonstrates how transition addition can cause activity reduction in out-of-equilibrium models, supported by a semi-mean-field approximation and numerical simulations.

Findings

Adding transitions can cause activity to vanish in certain models

Some models behave as expected, others exhibit jamming

Semi-mean-field approximation aligns qualitatively with simulations

Abstract

Adding transitions to an equilibrium system increases the activity. Naively, one would expect this to hold also in out of equilibrium systems. This surprising effect is caused by adding heretofore forbidden transitions into less and less active states. We demonstrate, using relatively simple models, how adding transitions to an out of equilibrium system may in fact reduce the activity and even cause it to vanish. We investigate six related kinetically-constrained lattice gas models, some of which behave as naively expected while others exhibit this non-intuitive behavior. We introduce a semi-mean-field approximation describing the models, which agrees qualitatively with our numerical simulation.